I have Server at hetzner.de, with a /29 subnet for running KVM-VMs. The VMs get network access via a bridge interface. I'm currently using two IPs from the subnet. The VM-host is running Ubuntu 12.04 kernel 3.2.0, as is one of the VMs, the other VM is running CentOS 5.8 kernel 2.6.18.

This setup was working flawlessly up until a few days ago, when I couldn't access the Ubuntu VM via the internet anymore. ping, ssh, http etc gave timeouts, so I accessed the VM via virt-viewer and tried to ping google.com: